1. Field of the Invention
The present invention relates to a laser working method for example a method for producing by such a laser working method an ink jet recording head for discharging an ink droplet and depositing such ink droplet on a recording medium, and an ink jet recording head produced by such a method. In particular, the present invention relates to a laser working method capable of working a worked article without fusion or thermal expansion therein and capable of precisely working a fine mask pattern in mask projection, a method for producing an ink jet recording head by such a laser working method, and an ink jet recording head thus produced.
2. Related Background Art
For minute working of a structured article requiring a fine structure and high precision, a laser working method employing an ultraviolet laser has been employed.
Such minute working can be exemplified by working of ink flow paths and ink discharge ports of an ink jet recording head.
The Japanese Patent Application Laid-Open No. 2-121842 or No. 2-121845 discloses high precision working of forming ink flow paths and ink discharge ports with an excimer laser which is a representative ultraviolet laser.
The excimer laser is capable of emitting ultraviolet light of a short pulse (15 to 35 ns) by discharge excitation of mixed gas of rare gas and halogen gas, with an oscillation energy of several hundred mJ/pulse and a pulse repeating frequency of 10 to 500 Hz. When the polymer resin surface is irradiated with a short-pulsed ultraviolet light of such high intensity, there is generated an ablative photodecomposition (APD) process in which the irradiated portion instantaneously decomposes and scatters with a plasma light emission and an impact sound, whereby so-called laser ablation working of polymer resin is made possible.
Among the conventional lasers employed for such working, the widely employed YAG laser can form a hole, but generates a coarse edge face, while the CO2 laser emitting infrared light is associated with a drawback of generating a crater around the formed hole. Such laser working methods are thermal working methods in which the working is achieved by converting optical energy into thermal energy, so that the shape of the worked article is often lost and fine working is difficult to achieve. On the other hand, the laser ablation working utilizing the excimer laser, based on sublimation etching by a photochemical reaction breaking the covalent bond of carbon atoms, does not easily break the shape of the worked article and can therefore achieve working of very high precision.
The laser ablation working method means a working method by sublimation, not through a liquid phase, by a laser.
Particularly in the field of ink jet technology, it is fresh in memory that the technology has undergone a remarkable progress to the present state by the adoption of the laser ablation working technology utilizing such excimer laser.
With the practical adoption of such laser working technology with excimer laser, there have been found the following phenomena.
The pulse oscillation time of the irradiating laser is about several ten nanoseconds in case of the excimer laser which is an ultraviolet laser or about 100 picoseconds to several nanoseconds in case of the YAG laser, but all the laser light falling on an article is not consumed for cleaving the covalent bonds of the atoms.
Because of the presence of such optical energy not consumed in cleaving the covalent bonds of the atoms, the laser worked portion of an article scatters before being completely decomposed, thereby forming by-products around the working area.
A part of the optical energy not consumed in cleaving the covalent bonds of the atoms is converted into thermal energy.
Also, as the energy density of the excimer laser remains at the level of 100 megawatts at maximum in the oscillation pulse, the subliming ablation working is not easily applicable to the materials of high thermal conductivity such as metals, ceramics or mineral substances (such as silicon) or materials of low light absorption such as quarts or glass, and can be principally employed for organic resinous materials.
These phenomena are unavoidable in using the excimer laser, and various technologies have been proposed to avoid the influences of these phenomena on the actual ink jet head.
For example a step of removing the by-products is executed, since the ink discharge ports may be clogged if the ink jet recording head is assembled while such by-products still remain.
Also, as the conversion of part of optical energy into thermal energy may cause thermal expansion or partial fusion of an article in the course of working, a material of a high glass transition point or a reduced working pitch is employed.
Since these technologies do not fundamentally resolve these phenomena, various limitations are practically imposed in the laser working.
On the other hand, a higher definition in the image quality is being required for the ink jet recording head, and the density of arrangement of the ink discharge ports or the ink flow paths, which has conventionally been in a range of from 300 to 400 dpi, is now required to be increased to 600 dpi, or even 1200 dpi.
Therefore, there is a demand for a method capable of forming the discharge ports and the ink flow paths with a small pitch or a small dimension, such as an arrangement pitch of 50 xcexcm or less and a working diameter of 20 xcexcm or less, with a high precision.
However the above-mentioned phenomena associated with the excimer laser become more conspicuous as the working pitch or the working diameter becomes smaller, and are posing limitations in producing the ink jet head of high precision as mentioned above.
In consideration of the foregoing, the present inventors, having recognized that the aforementioned phenomena are ascribale to the laser ablation working utilizing the ultraviolet laser exemplified by the excimer laser, have made intensive investigations not restricted in the field of the conventional technologies and have reached a novel laser ablation technology that is capable of fundamentally resolving these phenomena, also adapting to the minute working technologies ever advancing hereafter and also expanding the adaptability to various applications.
The present invention was made in view of the foregoing. An -object of the present invention is to provide a laser working method free from generation of by-products and fundamentally avoiding accumulation of thermal energy, generated in the course of laser working, in an article such as a resinous material (generally called xe2x80x9cworkpiecexe2x80x9d), thereby achieving highly precise working without fusion or thermal expansion of the article, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Another object of the present invention is to provide a laser working method capable of forming a minute structure in an article composed of plural materials by a simple working step, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Still another object of the present invention is to provide a laser working method capable of simplifying an alignment step, improving the precision such as the positional precision of an internally structured member and reducing the manufacturing cost, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
Still another object of the present invention is to provide a laser working method capable of improving the working efficiency by constructing an article so as to absorb the radiation energy of laser, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method.
The above-mentioned objects can be attained, according to the present invention, by a laser working method, a method for producing an ink jet recording head utilizing such laser working method, and an ink jet recording head produced by such producing method, featured as described in the following items (1) to (30):
(1) A laser working method for carrying out laser ablation working on an article by irradiating the article with laser light, which comprises, in working by projecting the laser light on a mask pattern, employing the laser light in a plurality of pulses having a very high energy density in space and time, as emitted from a laser oscillator that can oscillate with a pulse emission time not exceeding 1 picosecond, and dynamically changing a speckle interference image generated by light diffraction at the passing of the laser light through the mask pattern, thereby forming an integrated image of the speckle interference image and producing a pattern substantially the same as the mask pattern.
(2) A laser working method according to item (1), wherein the mask is displaced and vibrated in the direction of the optical axis to form the integrated image of the speckle interference image on the surface of the article.
(3) A laser working method according to item (2), wherein the displacement vibration of the mask is effected by a vibration actuator.
(4) A laser working method according to item (1), wherein the integrated image of the speckle interference image is formed on the surface of the article, by inserting a wavelength plate having a slope of at least from 0xcex to xcex/2 between the mask and a projection lens or between the projection lens and the article and carrying out laser irradiation while moving the wavelength plate so that light polarization is changed.
(5) A laser working method according to any of items (1) to (4), wherein a wavelength of the laser light is within a range of from 350 to 1000 nm.
(6) A laser working method according to any of items (1) to (5), wherein a pulse radiation time of the laser light is not more than 500 femtoseconds.
(7) A laser working method according to any of items (1) to (6), wherein the article is composed of a resinous material, Si or a Si compound.
(8) A laser working method according to any of items (1) to (7), wherein the laser oscillator is provided with a light propagation space compressing device.
(9) A laser working method according to item (8), wherein the light propagation space compressing device is composed of a chirping pulse generation means and a vertical mode synchronization means utilizing light wavelength dispersion characteristics.
(10) A method for producing an ink jet recording head comprising an ink discharge port for discharging an ink droplet to be deposited on a recording medium, a liquid chamber containing ink to be supplied to the ink discharge port, an ink flow path for communicating the liquid chamber with the ink discharge port, an energy generation element provided in a part of the ink flow path and generating energy for ink discharge, and an ink supply aperture for supplying ink from the outside to the liquid chamber, in which a member constituting at least a part of the ink passages of the ink jet recording head is worked by laser working, wherein:
in projecting laser light on a mask pattern, the laser working is carried out by using the laser light in a plurality of pulses having a very high energy density in space and time, as emitted from a laser oscillator that can oscillate with a pulse emission time not exceeding 1 picoseconds, and
a speckle interference image generated by light diffraction at the passing of the laser light through the mask pattern is dynamically changed, thereby forming an integrated image of the speckle interference image and producing a pattern substantially the same as the mask pattern.
(11) A method for producing an ink jet recording head according to item (10), wherein the mask is displaced and vibrated in the direction of the optical axis to form the integrated image of the speckle interference image on the surface of the ink jet recording head.
(12) A method for producing an ink jet recording head according to item (11), wherein the displacement vibration of the mask is effected by a vibration actuator.
(13) A method for producing an ink jet recording head according to item (10), wherein the integrated image of the speckle interference image is formed on the surface of the ink jet recording head, by inserting a wavelength plate having a slope of at least from 0xcex to xcex/2 between the mask and a projection lens or between the projection lens and the ink jet recording head and carrying out laser irradiation while moving the wavelength plate so that light polarization is changed.
(14) A method for producing an ink jet recording head according to items (10) to (12), wherein a plurality of recesses or penetrating holes constituting a part of the ink passage is formed simultaneously at a predetermined distance by laser light irradiation through a mask with a pattern having a plurality of apertures formed with a predetermined pitch.
(15) A method for producing an ink jet recording head according to item (14), wherein the recess is a groove to form the ink flow path.
(16) A method for producing an ink jet recording head according to item (14), wherein the penetrating hole is to form the discharge port.
(17) A method for producing an ink jet recording head according to any of items (10) to (16), wherein the wavelength of the laser light is within a range of from 350 to 1000 nm.
(18) A method for producing an ink jet recording head according to any of items (10) to (17), wherein a pulse radiation time of the laser light is not more than 500 femtoseconds.
(19) A method for producing an ink jet recording head according to any of items (10) to (18), wherein a member constituting at least a part of the ink passage including the discharge port, ink flow path, liquid chamber and ink supply aperture is composed of a resinous material.
(20) A method for producing an ink jet recording head according to any of items (10) to (18), wherein a member constituting at least a part of the ink passage including the discharge port, ink flow path, liquid chamber and ink supply aperture is composed of Si or a Si compound.
(21) A method for producing an ink jet recording head according to any one of items (10) to (20), wherein the laser oscillator is provided with a light propagation space compressing device.
(22) A method for producing an ink jet recording head according to item (21), wherein the light propagation space compressing device is composed of a chirping pulse generation means and a vertical mode synchronization means utilizing light wavelength dispersion characteristics.
(23) An ink jet recording head comprising an ink discharge port for discharging an ink droplet to be deposited on a recording medium, a liquid chamber containing ink to be supplied to the ink discharge port, an ink flow path for communicating the liquid chamber with the ink discharge port, an energy generation element provided in a part of the ink flow path and generating energy for ink discharge, and an ink supply aperture for supplying ink from the outside to the liquid chamber, in which a member constituting at least a part of the ink flow passages of the ink jet recording head is worked by laser working, wherein:
in projecting laser light on a mask pattern, the laser working is carried out by using the laser light in a plurality of pulses having a very high energy density in space and time, as emitted from a laser oscillator that can oscillate with a pulse emission time not exceeding 1 picosecond, and
a speckle interference image generated by light diffraction at the passing of the laser light through the mask pattern is dynamically changed, thereby forming an integrated image of the speckle interference image and working the member.
(24) An ink jet recording head according to item (23), having the member worked by displacing and vibrating the mask by a vibration actuator in the direction of the optical axis, thereby forming the integrated image of the speckle interference image on the worked surface of a workpiece.
(25) An ink jet recording head according to item (24), having the member worked by forming the integrated image of the speckle interference image on the surface of a workpiece, by inserting a wavelength plate having a slope of at least from 0xcex to xcex/2 between the mask and a projection lens or between the projection lens and the workpiece and carrying out laser irradiation while moving the wavelength plate so that light polarization is changed.
(26) An ink jet recording head according to items (23) to (25), wherein a plurality of recess or penetrating holes constituting a part of the ink passage is formed simultaneously at a predetermined distance by laser light irradiation through mask having a pattern of plural apertures formed with a predetermined pitch.
(27) An ink jet recording head according to item (26), wherein the recess is a groove to form the ink flow path.
(28) An ink jet recording head according to item (26), wherein the penetrating hole is to form the discharge port.
(29) An ink jet recording head according to any one of items (24) to (28), wherein a member constituting at least a part of the ink passage including the discharge port, ink flow path, liquid chamber and ink supply aperture is composed of a resinous material.
(30) An ink jet recording head according to any one of items (24) to (28), wherein a member constituting at least a part of the ink passage including the discharge port, ink flow path, liquid chamber and ink supply aperture is composed of Si or a Si compound.